Combine the soy sauce, vinegar, water, sugar, garlic and thyme in a deep nonreactive bowl large enough to hold the lamb. Whisk the ingredients together, add the lamb and turn over to coat with marinade on all sides. Cover tightly with plastic wrap and marinate in the refrigerator overnight turning at least once.

Heat the oven to 350°F and remove the lamb from the marinade to a roasting pan. Season well with salt and pepper and roast in the middle of the oven for about 1 hour or until an instant-read thermometer inserted in the center of the roast reaches 130 to 135°F. Remove lamb from the pan and allow to rest 30 minutes before slicing.

Serve the sliced lamb on a bed of Heirloom Grain and Bean Salad and drizzle with Chive Vinaigrette.